Seattle: Boeing's 747 jumbo jet, an aircraft that democratized global air travel in the 1970s but fell behind modern twin-engine passenger jets, has bounced back from near death to mark its 50-year flying anniversary on Saturday, thanks to a cargo market boom fuelled by online shopping.

Boeing's "Queen of the Skies" is the world's most easily recognized jetliner with its humped fuselage and four engines. It is now enjoying a second, perhaps less glamorous life, as a cargo mule for companies like United Parcel Service Inc.

"It's an efficiency machine for us," said Jim Mayer, a spokesman for UPS, the world's largest package deliverer.

UPS ordered 14 more 747-8 freighters in 2018, a lifeline that helps ease doubts over the future of the jumbo, which looks set to outlive its European competitor, Airbus SE's A380.

A 747 used by Air India. File photo

Airbus is looking "extremely seriously" at closing its superjumbo A380 factories sooner than expected, Reuters reported in January, after Dubai's Emirates indicated it might switch its A380 orders to the smaller A350.

Unlike the 747, Europe's superjumbo does not have a freighter version to help absorb slack demand.

Boeing had said in 2016 it could end 747 production amid falling orders and pricing pressure. Major US carriers like United Continental Holdings Inc and Delta Air Lines Inc have already said goodbye to the 747.

By keeping the 747 alive, Boeing avoids charges and layoffs for halting production at the mammoth wide-body plant outside Seattle.

It also shields newer programs like the 787 Dreamliner and the latest model of 777, which would have to bear a larger share of the plant's huge overhead if the 747 line went dark.

Still, the 747's extended lifespan could be tempered by US-China trade tensions and concerns about a broader economic slowdown threatening freighter demand.

Global air cargo rose 3.5 per cent in 2018 compared with 9.7 per cent in 2017, according to the latest data from the International Air Transport Association.

The 747, which had its maiden flight on February 9, 1969 and entered service on Pan American World Airways in January 1970, allowed for more affordable air travel due to its size and range.

It still flies passengers for Lufthansa, Korean Air and Air China, and does have one other role.

A British Airways Boeing 747 passenger jet takes off. Reuters

The US government asked Boeing in 2017 to repurpose two 747-8 jetliners for use as Air Force One by the US president. The two aircraft are due to be delivered by December 2024, painted red, white and blue.

The $3.9 billion contract followed President Donald Trump's objection to the $4 billion price tag of a previous Air Force One deal. He tweeted that "costs are out of control" and added "Cancel order!"